Punches and their associated dies have been used for decades in construction and industry to make holes in workpieces, such as sheet metal, for field installation of electrical, plumbing, and heating/AC equipment.
FIGS. 1-4 show a prior art punch 10 which is used for punching a hole through a workpiece, such as sheet metal. This punch 10 is disclosed in U.S. Pat. No. 4,543,722, the disclosure of which is incorporated herein by reference in its entirety. The punch 10 is used with a die 40 (only partially shown in FIG. 3) which is well-known in the art, as well as a draw shaft (not shown).
The punch 10 has a contoured working face 14 which reduces the peak punching force by first piercing the workpiece and then shearing the circumference of the hole. The contoured working face 14 of the punch 10 has a profiled leading edge 29, which includes piercing points P1, P2 and cutting surfaces 30b, 32b, which causes the slug or scrap which is punched in the workpiece to be torn in half, making it easy for the slug or scrap to be removed from the die 40.
The die 40 has a circular planar base wall 42 with a circular depending wall 44 extending from the perimeter of the base wall 42. A central passageway 46 extends through the axial center of the base wall 42. The size of the die 40 is dictated by the size of the punch 10 used.
If the punch 10 is advanced too far into the die 40, the leading edge 29 of the punch 10 “bottoms” in the die 40, i.e., the punch points P1, P2/cutting surfaces 30b, 32b come into contact with the base wall 42 of the die 40, and damage to the punch points P1, P2/cutting surfaces 30b, 32b can result. Actuation of the punch 10/die 40 with an electric or power hydraulic device can advance the punch 10 so rapidly that the user may not stop the punching cycle before the punch 10 “bottoms” in the die 40. For this reason, manufacturers of punches/dies have long recommended only manual actuation of the punches/dies with a wrench. Use of electrohydraulics has been discouraged to prevent damage to the punch.
Mechanical and electrical contractors are seeking ways to reduce the time for field installation of conduit, pipe, and round ductwork. As a result, power punching of holes in sheet metal is increasingly replacing the traditional manual wrench methods.
Punches and their associated dies are sold separately from the various battery, electric, hydraulic and mechanical devices which are used to actuate the punch relative to the die. There are battery and corded electric hydraulic pump/ram tools which attempt to stop the advancing of the punch when an internal pressure sensor detects the drop in force when the punching cycle is complete. These pressure drop sensors tend not to be completely reliable on thinner steels, softer materials (i.e. copper, aluminum), and for smaller hole diameters. Punching systems which incorporate an internal pressure sensor are expensive and may be justifiable only for larger construction jobs. In addition, many electricians make use of their existing all-purpose industrial hydraulic pumps without the pressure drop sensor to actuate knockout punches.
A punch and die are provided herein which has integral cutting edge protection which is independent of the various power driving systems. Other features and advantages of the present die will become apparent upon a reading of the attached specification, in combination with a study of the drawings.